EPR spectra and local lattice structure of Fe3+ impurity ions in ferroelectric LiNbO3

The optical absorption and EPR spectra of Fe3+ impurity ions doped in near stoichiometric LiNbO3 crystal are studied by diagonalizing the complete energy matrices for a d5 configuration ion in a trigonal ligand-field. By analyzing the optical absorption and EPR spectra simultaneously, the distortion parameters Δθ1 = 3.42°, Δθ2 = −7.22° are determined for Li+ substitutional position supported by ENDOR experiments. The theoretical results indicate that there exists a compressed distortion in LiNbO3:Fe3+ system, which may be ascribed to the fact that the radius of Fe3+ ion is slightly smaller than that of the host ion. Meanwhile, the local structure parameters R1 = 2.08A, R2 = 1.91A, θ1 = 47.99° and θ2 = 62.52° for the octahedral Fe3+ center in LiNbO3 crystal are also determined, which are close to that of the αFe2O3. The calculated transition energies of octahedral Fe3+ center in LiNbO3 are in good agreement with those of Fe3+ cations in other oxides due to the similar octahedral (FeO6)9− cluster.